Microwave preparation, structure and electrical properties of calcium–sodium–phosphate biosystem

The hydroxyapatite biomaterial (Ca10(PO4)6(OH)2 – HAP) is the main mineral constituent of teeth and bones, with excellent biocompatibility with hard and muscle tissues. These materials exhibit several problems of handling and fabrication, which can be overcome by mixing them with a suitable binder. In this study, a microwave process was used to produce hydroxyapatite using the starting materials CaCl2 and Na2HPO4 with previous precipitation. The mixture was exposed to microwave radiation for 5, 10, 15 and 20 min through domestic microwave ovens with an output power of 1 kW and frequency oscillation of 2.45 GHz. The samples were analyzed by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, dc conductivity and impedance spectroscopy. X-ray powder diffraction revealed the formation of HAP after 5 min of exposure. The presence of a low crystallinity state and the transition, with the rise of radiation exposure time, to a crystalline phase was related to the Ca/P mass and Ca/P atomic ratio. The presence of this low crystalline phase, detected by X-ray powder diffraction and scanning electron microscopy, seems to have a direct influence on electrical and dielectrical characteristics.